Gallium nitride (GaN) can be used in manufacturing high-speed or high-power integrated circuit devices. Gallium nitride is often desirable because it can withstand high operating temperatures and can provide high breakdown voltages compared to standard silicon devices. Gallium nitride can also typically provide good high-frequency performance. As a result, gallium nitride may be effectively used in applications such as high-power microwave applications (like in cellular base stations) and high-efficiency power regulation applications (like in electric vehicles).
Native gallium nitride substrates are not generally available. Instead, gallium nitride epitaxial layers are often formed over silicon-based substrates using metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (MOPVE), or metal-organic vapor phase epitaxy (MOPVE) techniques. Silicon carbide (SiC) substrates could be used here, but they are often expensive and limited in size. Ordinary silicon substrates could also be used here, but it is often difficult to form high-quality gallium nitride epitaxial layers over large silicon substrates, such as substrates with six or eight inch diameters. This could be due to a number of factors, such as high stress levels, large thermal expansion coefficient mismatches, high defect densities, and wafer bowing.
The inability to form thick high-quality gallium nitride layers can reduce the breakdown voltage of field effect transistors (FETs), high electron mobility transistors (HEMTs), or other devices formed using the gallium nitride layers. As a particular example, it may only be possible to form a gallium nitride layer that is 2-3 μm thick over a six-inch silicon wafer, which could provide a breakdown voltage of approximately 600V. It may not be possible to grow thicker gallium nitride layers in order to provide higher breakdown voltages. Even if it was possible, it would likely require special processing tools to further fabricate semiconductor devices using the gallium nitride layers.